CMR service is one of the most rapidly growing telecommunication services currently offered. (See, for example, "Surging, Price-Insensitive Demand Over Next Two Years and Strong Five-Year Picture Forecast for Cellular Industry Association, Which Sees Capacity Concerns Validated," TELECOMMUNICATIONS REPORTS, Aug. 15, 1988 (pp. 22, 23).) The technology underlying CMR service is exhaustively documented and well within the understanding of those possessed of ordinary skill in the art. Accordingly, a rigorous description of CMR technology will not be undertaken here, and the reader will be referred to the following representative publications, the contents of which are hereby incorporated by reference:
Arrendondo, G. A., J. C. Feggeler, and J. I. Smith. 1979. AMPS: Voice and Data Transmission, Bell System Technical Journal 58, no. 1 (January): 97. PA1 Bernard, Josef. 1987. The Cellular Connection. Mendocino, Calif.: Quantum Publishing. PA1 Bartee, T. C., ed. 1985. Data Communications, Networks, and Systems. Indianapolis: Howard W. Sams. PA1 Bartee, T. C., ed. 1986. Digital Communications. Indianapolis: Howard W. Sams PA1 Fluhr, Z. C., and P. T. Porter. 1979. AMPS: Control Architecture. Bell System Technical Journal 58, no. 7 (January): 43. PA1 Gibson, Stephen W. 1987. Cellular Mobile Radio Telephones. Englewood Cliffs: Prentice-Hall. PA1 IEEE Journal on Selected Areas in Communications. 1984. Special issue on mobile radio communications. See Hirono et al., Miki and Hata, and Suzuki et al. IEEE Journal on Selected Areas in Communications SAC-2, no. 4 (July). PA1 IEEE Transactions on Communications. 1973. Special joint issue on mobile radio communications. IEEE Transactions on Communications COM-21, no. 11 (November). PA1 Lee, W. C. Y. 1982. Mobile Communications Engineering. New York: McGraw-Hill. PA1 MacDonald, V. H. 1979. AMPS: The Cellular Concept. Bell System Technical Journal 58, no. 7 (January): 15.
Of course, one of the salient attractions of CMR service is that it affords the subscriber enhanced access to the public switched telephone network (PSTN), thereby enabling the subscriber both to place and to receive telephone calls at times when he would otherwise have been inaccessible, that is, at times when he is constrained to the confines of an automobile. The accessibility afforded by CMR technology is further enhanced by the availability of transportable CMR units that may be removed from the automobile and carried by the subscriber.
However, one characteristic of the existing CMR system is that this high degree of accessibility is approachable only when the subscriber is physically present within the range covered by his home service area. The subscriber's ability to receive incoming calls outside his home service area has heretofore been severely restricted in ways that will be described below, but are largely circumvented by the instant invention. (A subscriber using, or attempting to use, his cellular phone in a service area outside his home service area is aid to be "roaming" and is, at least for the purposes of this document, referred to as a "roamer".)
In fact, although it might be assumed that the subscriber will not always be aware that he has travelled beyond the range of his home service area, the cellular system has been designed to detect this situation and to so apprise the subscriber.
Briefly, each cellular system has been uniquely assigned a System ID (SID). Electrical signals corresponding to each cellular system's SID are continually transmitted by that system over a control channel separate from the channel used to provide voice communications. The SID of the system from which a particular subscriber has agreed to acquire CMR services is programmed into a Numerical Assignment Module (NAM) incorporated into the subscriber's mobile unit. When a subscriber's mobile unit is "powered up," it reads a System Parameter Overhead Message that includes the fifteen-bit SID of the system whose signal the mobile unit is receiving. The mobile unit then compares the transmitted SID to the SID programmed in its NAM to determine identically. If the unit determines lack of identicality, a "ROAM" light is activated on the control head associated with the mobile unit. In this manner, the subscriber is made aware that his mobile unit has "seized" a system other than the system on which he is an authorized subscriber.
A roamer who desires to place an outgoing call to the system in the area in which he is roaming need only remember to first dial the area code of that system. Calls placed to the subscriber's home system do not require the dialing of a prefatory area code.
The procedure for receiving incoming calls, however, is substantially more cumbersome. An essential element of the roamer's ability to receive incoming calls is that would-be third-party callers to him need to know in which system the subscriber is physically available. Unanswered calls placed to the subscriber's home number will be answered with a message indicating that the subscriber cannot be found. What the caller needs to know, then, is what CMR system the roamer is using and the procedure for accessing the subscriber through the facilities of that system. That is, the caller must know the roamer's itinerary and the roamer access number of the system the roamer is using. The major service areas each have a ten-digit roamer access number. Areas in which service is provided by both a wireline and a nonwireline carrier, of course, have two roamer access numbers, one corresponding to the wireline carrier and one corresponding to the nonwireline carrier.
Armed with this information, the would-be caller must first dial the ten-digit roamer access number of the system he expects the roamer to be using. After a short pause followed by a tone, the caller must then dial the roamer's home number, including his home area code. In some services areas, this cumbersome and demanding procedure is exacerbated by the need for the subscriber to prearrange, with the CMR service provider in the "foreign" area, the right to have incoming calls delivered.
Even when the above-mentioned procedural hurdles have been surmounted, the foreign-area service provider may be disinclined to have (or technically incapable of having) the applicable service charges applied to the subscriber's home service area bill, and the charge will need to be prepaid or applied to an acceptable credit card.
In a manner that will be made clear by the detailed Description set forth below, the above-indicated limitation of the CMR system, as it has been heretofore implemented, is cured by the invention underlying the Follow-Me-Roaming (SM) Cellular Mobile Radiotelephone Service. ("Follow-Me-Roaming" is a service mark of GTE Mobilnet Incorporated. At appropriate occurrences throughout the remainder of this document, various constituent elements of the combined hardware and software system that implements that service are referred to in conjunction with the use of the acronym "FMR".)